1. Field of the Invention
The present invention relates generally to an automatic paper feeding device for use in, for example, a facsimile machine, and more specifically, to the up and down movement mechanism of a sending out roller used for sending paper, an automatic paper feeding mechanism for ensuring separate paper feeding, etc.
2. Description of the Background Art
Conventionally, the following mechanism is known as an automatic paper feeding mechanism for feeding original paper in, for example, a facsimile machine. More specifically, the mechanism, as shown in FIGS. 10 and 11, includes a sending out roller 50, and a paper feeding roller 51 provided in the machine at a further inner part than this sending out roller 50.
These rollers 50 and 51 are pivotably supported on a pivotable member of channel shape (hereinafter referred to pivotable member) which is disposed below an insert guide plate 56, and rotatably coupled by gears 53, 54, and 55. An entrance 31 for inserting original paper 32 is formed between insert guide plate 56 and sending out roller 50.
The circumferential surface of paper feeding roller 51 abuts upon a separation rubber plate 56a provided at the lower surface of insert guide plate 56. One end of the supporting shaft 51a of paper feeding roller 51 extends from pivotable member 52 and coupled to a driving source (not shown) provided on the side of the machine body.
Such coupling of the supporting shaft 51a of paper feeding roller 51 to the machine body side allows the pivotal movement of pivotable member 52 around supporting shaft 51a, and a DC solenoid 57 is provided as means for pivoting the angle. DC solenoid 57 is attached to the side of the machine body, and the tip end of its expansion/contraction rod 57a is connected to pivotable member 52. Therefore, when an operation signal is supplied to DC solenoid 57, expansion/contraction rod 57a contracts to pivotable member 52 and lifts sending out roller 50.
In the figures, the reference numeral 58 designates a conveying roller for sending original paper 32 sent into the machine by paper feeding roller 51 further inside the machine.
According to such an automatic paper feeding mechanism, a plurality of sheets of original paper 32 set at entrance 31 are separated from the lower end side by driving rotating of sending out roller 50 lifted (elevated) by DC solenoid 57, and sent to the side of paper feeding roller 51 on a one-by-one sheet basis. The sheets of original paper 32 are sent further into the machine by driving paper feeding roller 51 to rotate.
When sending of all sheets of a sheaf of original paper 32 is completed, DC solenoid 57 expands expansion/contraction rod 57a to lower pivotable member 52, and opens entrance 31 so that the next sheaf of original paper 32 can be inserted.
In an automatic paper feeding mechanism, sheets of original paper 32 should be fed at regular intervals. Otherwise the machine can not separately identify sheets of original paper 32. Therefore, in a conventional automatic paper feeding mechanism, for example, a method is employed by which a sheet of original paper 32 at the bottom layer is separated by the striking out of sending out roller 50 and sheets of original paper 32 are sorted out by separation rubber plate 56a provided at the upper part of paper feeding roller 51. It is however difficult to successfully achieve separate feeding of paper according to such a method.
This is because due to the structure of DC solenoid 57, it is difficult to change the amount of contraction and the position to which sending out roller 50 is elevated is constant. However, sending out roller 50 is naturally elevated to different positions between the state where a large number of sheets of original paper 32 are stacked thereon and that where a small number of sheets of original paper 32 are stacked thereon. As a result, the conventional automatic paper feeding mechanism is encountered with difference in interlayer pressing force by DC solenoid 57 between a sheaf of a large number of sheets of original paper 32 and a sheaf of a small number of sheets of original paper 32. Particularly, in the case of the original paper 32 with a large number of sheets piled thereon, pressing force between the sheets of original paper 32 increases, rendering the friction force between the sheets of original paper 32 larger than the striking force of sending out roller 50, resulting in original paper 32 being too heavy to be sent.
Furthermore, DC solenoid 57 is sensitive to temperature because of its structure, its magnetic force changes in response to temperature change, and especially degrades with temperature rise. Construction of an automatic paper feeding mechanism using DC solenoid 57 with such a property makes it difficult to ensure separate feeding of paper due to its unstable sending of original paper 32.
Furthermore, DC solenoid 57 is a relatively expensive part for a striking noise it creates when the magnetic force takes effect and requires a driving circuit (not shown) for its driving, resulting in increase in the number of parts and costs.